Devices of the type to which this invention relates as heretofore known included a manually slidable member mounted in a body member that could be affixed to a wall or could be hand-held. On the body was a permanently mounted receptacle or cartridge for mercury and a removable or replaceable cartridge for silver alloy pellets. The slidable member in one position received a dosage of one pellet and a dosage of a predetermined adjustable amount of mercury. The permanent mercury reservoir was covered by a cap with an air vent hole which had to be kept closed during loading of the alloy pellets.
One example of such a prior device is disclosed in the De Gon U.S. Pat. No. 3,168,213 issued Feb. 2, 1965.
Among the disadvantages of such prior devices are liability of mercury spillage if the device was moved from horizontal upright position either inadvertently or purposely without closing the vent hole with a finger or in some other way; oxidation of the mercury through the vent hole; contamination of the working mechanism and parts by mercury oxidation; contamination of the finger used to close the vent hole when the device is moved from horizontal position; inability to lay the device on its side or place it upside down or tilt it in any plane during handling; liability of inadvertent or accidental operation of the device without a receiving capsule in place to catch the mercury and pellet, resulting in discharge on the floor.